The only thing a pc has going for it is you can usually upgrade it. However that can be costly too. Because some upgrades require you to upgrade other things just so newer things can work at their full potential. A decent gaming pc is going to cost you no matter what. Build your own beast and your still looking at around a grand and then still have to upgrade it every couple of years.
It's not just the ability to upgrade. You have much more freedom with the PC (both from the development side and the gamer side). Everyone isn't constricted to the same hardware and guidelines set forth by MS or Sony. Most people already have a reason to have a good computer, so why not make it a little better so that you can play games on it too? I really enjoy making high resolution wallpapers in Photoshop now. Before everything would go so slowly and I would just get tired of waiting for everything to load.
As for the cost, I spent less than a grand on the PC I built years ago and it still runs any game at max settings (which I don't even care about because I prefer the lowest settings :D). I haven't had to upgrade anything and I don't think that I will for another 2 or 3 years at least. By then I can justify spending another $300 because I will have avoided spending that on a new console.
What's the betting all these * I'm selling my 360 for a p.c* people will get the next- box? Rather good I say.
Kinda like the odds on you buying the next COD?